The present invention relates to a method and a device for intermittently injecting fuel into a combustion chamber of a combustion engine, wherein a closing and an opening of a valve needle of an injection valve is made possible exclusively by the interaction of a force source means acting in a closing position of the valve and a fuel pressure force acting on the valve needle.
In an injection valve, known from DE-OS 22 42 344, the injection process is exclusively controlled by the forces acting on the valve needle. On the one hand, the valve needle is maintained in its closing position by a pressure spring, on the other hand, the pressure exerted on the valve needle by the fuel pumped into the valve via the injection pump acts to lift the valve needle. In order to realize higher injection pressures without the need of increasing the force of the pressure spring above a reasonable value, the spring is assisted by an auxiliary piston acting in the closing position of the valve needle. When the pressure generated by the fuel exceeds the force of the pressure spring, fuel is injected into the combustion chamber of the combustion engine via an injection bore opened by the fuel pressure. When the pressure decreases, the force of the pressure spring and the auxiliary piston close the valve needle again. This known injection process, however, does not allow for multiple controlled opening and closing steps during one working cycle.
The higher requirements for cleaner exhaust gases may not be satisfied with the injection methods of the conventional injection valves. The exhaust fumes of Diesel engines must be reduced in their CH-contents as well as their carcinogenic soot particle contents that cause black exhaust fumes. At the same time, the NO.sub.X contents and the combustion noise must be reduced. These are, in part, quite contrary demands which may not be overcome by conventional injection methods
It is therefore an object of the present invention to improve the aforementioned known methods and devices such that an injection method which allows for a control of the mixture formation process and the quality of the combustion process, which depends on the mixture formation process, is provided, whereby the contents of CH and soot may be decreased without increasing the NO.sub.X contents and, at the same time, the combustion noise level is reduced to a minimum.